Zeleke Mekuriaw Zeleke

Abstract

Records of 326 Somali goats born from 1994 to 2004 in
eastern Ethiopia were used to assess effects of major environmental factors on
growth and survival traits. Year of birth had significant effect (P<0.01) on
birth weight, pre-weaning daily weight gain and weaning weight of kids.

Introduction

Goats are known to be
potential genetic resources for meat, milk, skin and fiber throughout tropical
and developing countries. Goats play an important role in generating employment,
income, capital storage and improving household nutrition. Being small in size,
they may not require large housing space per head compared to cattle and can
easily be handled and managed by women and children. Goats in Ethiopia with the
estimated total population of 18.5 million (CSA 2007) make a major contribution
towards meat, milk and skin production. They are more dominant in lowland areas
of Ethiopia, which encompasses more than 60% of the total landmass of the
country. In these lowland areas, Somali goats are one of the known breeds reared
by pastoral and agro-pastoral societies for meat and milk production purposes
(FARM-Africa 1996). In these areas, goats are the most important species for
milk next to camels. It was also reported that goats are the most common animals
sold by pastoral households for immediate cash income such as for purchase of
food items. They are also the major species slaughtered at home to be consumed
by the family (FARM-Africa 1996; Baars 2000), which indicates their significant
role in household nutrition and food security of the pastoral society.

Even though growth performance and survival rates are the
most important production traits for successful animal production for whatever
purpose, very little is known about these traits for Somali goat under extensive
management conditions of Ethiopia. Therefore, the current study is intended to
assess the effect of some environmental factors on pre-weaning growth
performance and mortality rates of Somali goats.

Material and methods

The study was conducted at Alemaya University, Eastern
Ethiopia. The University is located at 9024”N latitude and 4105”E
longitude, and at an altitude of 1980m above sea level. According to Alemaya
University’s meteorological data of 12 years (1992-2004), the area enjoys a
moderate average temperature of 16ºC, and the mean maximum and minimum annual
temperatures of 24.02 and 9.73 ºC, respectively. The annual rainfall, which
fluctuates from year to year, ranges between 507.30-995.40mm. The pattern of
rainfall is bimodal type consisting of short rainy season occurring from end of
April to end of June and main rainy season from July to beginning of October.
The dominant pasture types consist of
Hyparrhenia species, Cyndon dactylon, Sporobulus africanus and Pennisetun
species (Mengestu and Asnakeh 1986).

The Somali goat breed is found in Somalia, Ethiopia and
North-east Kenya (Mason 1996). The breed is used primarily for meat production.
These goats are predominantly white in colour, but some individuals have colored
spots or patches; the males are horned and the females are either horned or
polled.

The goats used for this study were managed at extensive
conditions. The animals were allowed to graze 8 hours a day (8h00-12h00 and
14h00-18h00) on legume-grass-mixed natural pasture. In addition to grazing,
lactating goats were occasionally provided with less than half a kilogram of
brewer’s grain per head per day in the afternoon after grazing. When brewer’s
grain is not available, they are given approximately 200-300 g of wheat bran per
head per day. Mineral lick and water were available ad libitum. All the goats
were provided with shelter during night. Kids were allowed to suckle their dams
up to the age of four months.

Records of 326 goats born from 1994 to 2004 were used for
the study. Birth date, birth weight, litter size, sex of kids and age of dams
were recorded for each kid during this period. Furthermore, body weight of kids
was measured fortnightly using weighing balance. Death of kids was also recorded
as it occurred.

The effects of environmental factors on birth weight,
average pre-weaning daily weight gain, and weaning weight of kids were analyzed
using General Linear Model (GLM) procedures of SAS (SAS 1999) whereas mortality
rates were analyzed using CATMOD procedures of the same software.

Results and discussion

Birth weight

The overall mean birth weight of Somali goats obtained in
the present study was 3.19 kg, which is inline with the report of Abebe (1996),
who indicated the birth weight of the same breed of goats in Awasa University,
Ethiopia, to be 3.05 kg. However, lower birth weights than the present finding
had been documented by Das et al (1994) for Tanzanian goats and Liu et al
(2005) for Angora goats.

The effects of year of birth, sex of kids, parity of dams
and litter size on birth weight are indicated in Table 1.

Table 1.
Effect of different factors on birth weight (g) of kids

Factor

N

Birth weight (Mean±SE)

Year of Birth

**

1994

4

3.50±
0.51a

1995

60

3.19±0.20
abc

1996

62

3.29±0.20
ab

1997

53

3.02±0.20
abc

1998

18

3.38±0.21ab

1999

25

3.38±0.20ab

2000

37

3.58±0.18a

2001

22

2.84±0.21bc

2002

30

2.92±0.21bc

2003

8

3.18±0.25abc

2004

7

2.64±0.25c

Season

NS

Short rainy

51

3.22±0.19a

Main rainy

105

3.25±0.19a

Dry

170

3.14±0.18a

Sex

**

Male

158

3.35±0.18a

Female

168

3.04±0.18b

Parity

**

1

105

3.18 ±
0.19ab

2

93

3.28±0.18a

3

80

3.39±0.21a

4

34

3.04±0.19b

5

14

2.98±0.23c

Birth type

***

Single

319

3.17±
0.06a

Twin

7

2.30±0.20b

Overall mean

3.19

a b c Means with different
superscript letters in a column under the same factor differ
significantly (P<0.01)N= Number of
observations; NS= Non significant; **= highly
significant

Year of birth had
significant (P<0.01) effect on birth weight of kids. The significant influence
of year of birth on birth weight of kids was also reported in previous studies
(Gifford et al 1990; Liu et al2005). As birth year is a complex variable
encompassing conditions of climate, feeding and management, the variation in
birth weights may be related to the variation of natural environments, feed
availability, management methods and body conditions of dams. The poor body
condition of dams may be a factor responsible for a reduced birth weight of kids
in some years. Even though the effect of year of birth on kid weight at birth is
not persistent, the general trend indicates that kids born in later years have
the least birth weights as compared to kids born in earlier years. This may be
due to deterioration of grazing land of the farm as the flock size increases
without proportionate increment in farmland or improved productivity per unit of
land.

Season of birth had no statistically significant effect
(P>0.05) on birth weight. The possible reason for lack of significant influence
of season on birth weight of kids may be availability of hay and concentrate
supplement to the dams during the dearth of browse.

The other non-genetic factor which significantly (P<0.01)
affected birth weight was sex of kids. In this study, males had significantly
(P<0.01) heavier birth weights than female kids. This is in agreement with
reports of Gerstmayr and Horst (1995), Bhoite et al (1996), Husein et al (1996)
and Liu et al (2005).

Similarly, the parity of dams had significant (P<0.01)
effect on birth weight of kids. Kids born from dams of fifth parity had lighter
(P<0.01) weights at birth compared to kids born from dams of first to fourth
parities. Kids born from fourth parity of dams also had significantly (P<0.01)
lighter weights at birth as compared to kids born from second and third parity
groups. In general, there is an increasing trend in birth weight of kids as the
parity of does advances from the first to third. Thereafter, the birth weights
of kids declined. Similar results were reported by previous workers
(Gifford et al 1990; Liu et al2005) concerning the effect of parity of
dams on birth weight of kids. The reason for the decline of the birth weight
beyond third parity groups of dams may be due to wear of teeth and consequent
loss of body condition of dams and hence retarded growth rate of fetus. Based on
the result of this finding, culling of dams beyond fourth parity can be
suggested.

Birth type was also found to have significant (P<0.01)
effect on birth weight of kids. In this case, single born kids had heavier birth
weights as compared to twins. The heavier birth weights recorded for single born
kids as compared to twins is in agreement with reports of Gifford et al (1990)
and Husein et al (1996). The probable reason for heavier birth weights of single
born kids is due to absence of intra-uterine nutritional and space competition
in single born kids unlike that of twin born kids. Robinson et al (1977)
reported that for lambs in utero, as the number of fetuses increase, the number
of caruncles attached to each foetus decreases, thus reducing the feed supply to
the foetus and hence reduction in the birth weight of the lambs.

Pre-weaning growth rate

Table 2.
Effect of different factors on average pre-weaning daily weight
gain (g) of kids

Factor

N

ADWG (Mean±SE)

Year of birth

***

1994

4

102.35±19.78a

1995

60

83.94±7.93ab

1996

62

68.10±7.66bc

1997

53

68.07±7.58
bc

1998

18

65.56±8.22
bc

1999

25

82.38±7.73ab

2000

37

77.84±6.97b

2001

22

59.34±8.07C

2002

30

12.50±8.01d

2003

8

10.56 ±9.81d

2004

7

15.47±9.59d

Season of birth

NS

Short rainy

51

62.87±7.40

Main rainy

105

57.56±7.20

Dry

170

55.77±7.13

Sex

**

Male

158

61.60±7.06a

Female

168

55.87±7.15b

Parity

NS

1

105

61.15±7.42

2

93

59.84±7.10

3

80

57.29±7.41

4

34

57.62±8.07

5

14

57.78±8.80

Birth type

**

Single

319

55.80±2.22a

Twin

7

47.31±7.92b

Overall mean

61.25

a b c Means with different
superscript letters in a column under the same factor differ
significantly (P<0.01); N= Number of
observations; NS= Non significant;
**= highly
significant; ADWG=Average daily weight gain

The pre-weaning weight gain obtained in this study
was lower than the one reported by Abebe (1996) for the same breed of goat (76
g/day). Lower pre-weaning daily weight gains than the present study was also
reported by Husein et al (1996) for Black Bengal goats (39.50±1.91
g/day). The variation in pre-weaning weight gain might have been emanated from
management difference of both dams and kids at early age.

Year of birth, sex and birth type of kids had significant
(P<0.01) effect on pre-weaning daily weight gain. There was a declining trend in
pre-weaning daily weight gain of kids from year 1994 to 2004; the least mean
daily weight gain being in year 2004. This indicates that there is deterioration
in feeding management of the flock in later years. Formerly, the goat farm had
been managed by FARM Africa, which is non-governmental organization. Later on,
it was handed over to Alemaya University. The overall input of production
invested on the same farm, even if difficult to quantify, differs between these
to institutions. The significant effect of year on weight gain of kids was
reported by Gifford et al (1990) and Liu et al (2005).

In this study, male kids gained significantly (P<0.01)
higher daily weights as compared to female kids. The pattern of live weight
change of male and female kids is indicated in figure 1.

Figure 1.
Effect of sex on
pre-weaning growth rates of Somali goats

The higher daily weight
gains in male kids than in females is in agreement with the reports of Husein et
al (1996). This is a natural phenomenon that male kids grow faster than females,
as their mature weight is also heavier.

Although there is a tendency of relatively higher daily
weight gains in kids born during rainy seasons as compared to dry season (figure
2), the difference was not statistically significant.

Figure 2. Effect of season of
birth on pre-weaning growth pattern of Somali goats

Parity of dams had significant (P<0.01) influence on
pre-weaning daily weight gain of kids. As the parity of dams advanced the
pre-weaning daily weight gain of kids declined. The significant influence of
parity of dam on pre-weaning daily weight gain of kids is in compliance with the
findings of Husein et al (1996) and Liu et al (2005). The likely reason for the
decline of pre-weaning daily weight gain of kids as the parity of their dams
advanced is due to a reduction in milk production performance of their dams.

Single born kids gained significantly (P<0.01) higher
daily weights as compared to twins, which is inline with the findings of Husein
et al (1996). The higher daily weight gains attained in single born kids is due
to relatively higher amount of milk consumed per kid as there is no competition
for dam’s milk. To improve weight gain in twin born kids, provision of special
feeding management such as creep feeding may be required. The growth pattern of
single born and twin kids is indicated in figure 3.

The overall mean weight at weaning (end of forth month of
age) was 11.67 kg. The value for live weight at weaning in this study is inline
with the reports of Das et al (1994), who reported 11.14±0.15
kg in Tanzania.

Year of kidding, sex of kids and birth type had
significant (P<0.01) effects on weaning weight (Table 3).

a b c Means with different
superscript letters in a column under the same factor differ
significantly (P<0.01)N= Number of
observations, NS= Non significant, **= highly
significant

There are inconsistent
variations in weaning weight of kids between years; the highest and the least
weaning weight being recorded in 1994 (15kg) and 2002 (9.65), respectively. This
may be due to variations in feed availability between years as distribution and
amount of rainfall also varies among years.

In this study males attained significantly (P<0.01)
heavier weights at weaning than female kids, implying that sex effects exist
even before the age of puberty. This is a natural phenomenon that males do have
faster growth rate and heavier weights at maturity than female animals. Similar
influences of age of animals on growth rates had also been reported by Bell et
al (1970) and Das et al(1994).

Similarly, single born kids weighed significantly (P<0.01)
higher than twins for the reason that the former consume dam’s milk alone
whereas the latter ones shared limited amount of milk between two kids.

Pre-weaning mortality rate

The overall mean pre-weaning mortality rate of Somali goat
kids and factors affecting it are indicated in Table 4.

a b c Means with different
superscript letters in a column under the same factor differ
significantly (P<0.01)

N1= Number of kids
born; N2= Number of kids died before the age of 4 months;
NS= Non significant; **= highly significant

The overall pre-weaning
mortality rate of kids in the present study was 11.52% (31/269). Out of 31
deaths encountered before four months of age, 11 deaths occurred within two
weeks of age. It seems that the first two weeks post kidding are critical
periods which determinately affect the survival rate of kids. The mortality rate
encountered in the present study is lower than the values reported by Awemu et
al (1999) for Red Sokoto goats in Nigeria (38%) and Husein et al(1995)
for Black Bengal kids in Bangladesh (28.3%).

Season of birth kids did not demonstrate any significant
effect on pre-weaning mortality rate contrary to findings of Husein et al
(1995), who reported significantly higher survival rates of kids born in rainy
season compared to those born during dry season. Absence of significant
difference in pre-weaning mortality rate due to season in the present study may
be due to provision of supplementary feed and shelter for goats which minimizes
nutritional variations and direct influence of weather factors such as ambient
temperature and humidity among seasons.

In this study, sex of kids did not show any significant
influence on pre-weaning mortality rate of kids which is inline with the
findings of Awemu et al (1999). Other previous findings (Husein et al 1995;
Alexandre et al 1999), however, indicated higher mortality rates in male kids as
compared to female kids. Ebozoje and Ngere (1995) also reported that females had
higher mortality rate than males in West African dwarf goats. Absence of
significant difference in mortality rate due to sex of kids in the present study
indicates lack of preferential management for female kids, as production
objective of Somali goats is both for milk and meat production.

Parity of dam and birth weight of kids had significant
(P<0.01) effects on pre-weaning mortality rates of kids. Significantly (P<0.01)
fewer number of kids born from dams of first and second parities died before
weaning age compared to kids born from the later parities. The pre-weaning
mortality rates of kids born from third and fourth parity groups of dams were
intermediate. The highest (P<0.01) number of pre-weaning mortality was
encountered in kids born from dams of fifth parity. The occurrence of higher
pre-weaning mortality rates in kids born from fifth parity dams in this study is
contrary to the findings of Husein et al (1995), who reported absence of
significant effect of parity on survival rates in Black Bengal kids. Awemu et al
(1999) also reported higher survival rate in Sokoto kids born from sixth parity
dams. The possible reason for the increased incidence of pre-weaning mortality
rates in kids born from fifth parity dams in the present finding may be due to
unsuitable uterine environment for the proper growth of the fetus and /or
reduced milk yield post-kidding due to old age.

Birth weight of kids affected (P<0.01) mortality rate. The
maximum mortality rate (75%) was recorded from kids weighing 1.5 kg or less at
birth followed by kids weighing 1.5-2kg. The least mortality rate was recorded
in kids with 3-4 kg at birth. Though not statistically significant, there is a
tendency of increasing in mortality rate when birth weight exceeds 4 kg (figure
4).

The occurrence of increased incidence of mortality in kids born with lower
birth weights is in compliance with the findings of Husein et al (1995). The
probable reason for higher rate of pre-weaning mortality of kids with lighter
birth weights is due to inadequate body reserves at birth to withstand
environmental stress. Again the scaling up of mortality rate in kids heavier
than 4 kg at birth may be due to difficulty during birth and/or inadequacy of
milk from their dams to satisfy their demand to maintain their higher body mass.
Improved management conditions which would help maintain optimum body condition
of dams to obtain kids with reasonable birth weights could be suggested.

In the present study, the type of birth significantly
(P<0.01) affected pre-weaning mortality rates of kids. Significantly
higher number of twin born kids died before weaning as compared to single born
kids. The higher incidence of mortality in twin born than single born kids is
inline with previous findings (Wilson and Light 1986; Awemu et al 1999). The
competition for limited nutrients in the uterus and for milk after birth may be
reasons for higher incidence of pre-weaning mortality in twin born kids.

Preferential feeding care should be given to twins
and their dams in order to mitigate inferior birth weights, pre-weaning growth
rates, weaning weights and higher pre-weaning mortality rates observed in twin
born kids as compared to single born kids.